I suppose they would be telling themselves that they are avoiding situations where parents "shop" for the "right" results. In most areas, I cannot believe that would be that much of an issue. Otherwise, the only explanation I can come up with is they are control freaks. ;-)
In your case, it seems very odd that they won't accept nationally-recognized tests (MAP, EXPLORE). I would be very tempted to ask "what are your district's reasons for not accepting tests administered elsewhere?" because I would be soooo curious as to what they'd say.
